My boat has a all stock 380HP 454 Mag EFI with thru-hull. What is the best way to get a reliable 600+ HP. I originally thought of a procharger, but have been thinking of pulling my 454mag and just poking in someone elses crate motor. I have no problem building a motor, but is a 454 bowtie block a good foundation to build a reliable motor, or should I get a big CID motor with more torque?

procharger, whipplecharger...I like that idea. I have never seen a procharger with a closed cooling system though (just wondering to myself).

If your motor is a 454MAG EFI the block is not a Bowtie.
The only naturally aspirated Merc motor with a Bowtie block is the Bulldog. The Mag EFI is a standard Gen VI block.
That doesn't mean it's not a good foundation for a 600hp motor though. You could start with a 4.25 stroker assembly and a good bore will make a good 496 stroker motor that some here have made some really good numbers with.

Dave

I thought there would be more guys pulling for sticking in a crate motor than building one from my 454.

You just have to weigh the cost and end result your after.
Using yours is just one option of many as you'll find out here shortly

Talk to dean gellner aka Mrhorsepower1 on here, you can make a nice n/a 540 out of your gen VI with some dart pro one heads and get 650 HP out of it. Just my 2 cents

You need a 502 block to make a 540.

Here is what I did. I started with a 454 bored and stroked it to a 489. New exhaust with long risers (no silent choice), RMbuilder custom cam. Good reliable 500HP. If you want more sell what you have and drop in a 540 or 572, start with a Dart or Merlin tall deck. You can easily build 600-650HP with that.

buy a 525

Sell what you have and start from scratch, been there. I did the Procharger and had good results with it but you will be better off starting from scratch with a 540. I added blowers, heads etc to some carbed 454 mags with good results. Both are options, but the 540 will be cheaper and more reliable down the road. A lot of stuff will have to be changed to do the Procharger right. If you build your 454 into more you will have a bunch of parts that you will have to give away. Again start from scratch and build it right.